During oilfield operations, mercury and mercury salts naturally present in geological formations may accumulate on the surfaces of pipes and vessels over time. This can present a significant safety risk to workers that may be exposed to mercury through skin contact with liquid mercury or inhalation of mercury vapors. As such, mercury is considered a hazardous substance and its safe removal and disposal is a safety priority.
At present the available methods for removing liquid mercury are limited and unsatisfactory. Mercury is insoluble in most solvents and is sparingly soluble in concentrated acids, including nitric acid, sulfuric acid, and aqua regia, which creates challenges in the removal and transport of mercury contaminants. However, the use of acid treatments to clean up mercury spills and surface contamination is disfavored because, in addition to the safety hazards to workers, acid treatments may corrode steel surfaces present on most downhole tools. Moreover, mercury cannot be easily removed using vacuum devices because during suction and filtration fine droplets of mercury and vapor are formed and may be released into the surroundings, exacerbating the problem of contamination.
Other approaches to mercury decontamination also include combining elemental sulfur with the mercury to form mercuric sulfide or cinnabar; a sparingly soluble mineral solid that is much safer to handle due to the reduced inhalation hazard of the solid with respect to elemental mercury. However, although mercury and sulfur combine to form cinnabar, the homogenous reaction of liquid mercury and powdered sulfur may often require physical intervention such as agitation, milling, and/or mixing. Thus, such approaches are limited in their effectiveness and overall reduction of the dangers posed by the presence of toxic mercury vapors.